For a so-called “RF over Glass” network, RF signals are carried through fiber optic cables on light beams as optical signals. In order to accommodate a potentially large number of different transmitters on a same network, the optical signals are queued in accordance with a standard protocol (e.g. DOCSIS 3.0). A consequence of this queuing is that each transmitter in a network will have its own “quiet time” as other transmitters are given access to the network. However, in order to be ready for a next transmission, light sources in a transmitter for generating the carrier beam have remained partially ON during the “quiet time”. This increases the transmission background noise when multiple transmitters are combined into a single fiber network.
Heretofore, the initiation of an RF transmission onto a fiber-optic network has been dependent on characteristics of the particular signal. Specifically, when there is high power in an RF signal, the turn-on time is relatively short. On the other hand, when there is low signal power, the turn-on time is extended. Thus, the turn-on time for optical transmissions can vary significantly from signal to signal, with possibly disruptive consequences. For instance, if the rise in the optical carrier power for an optical signal is too fast, dither may be introduced which can result in missing portions of the RF signal. However, if the rise in optical power is too slow, some of the RF signal may actually be lost. Neither case is acceptable.
Typical of the signal transmission protocols presently being used for “RF over Glass” networks is the use of a “burst mode” operation. As the name implies, a “burst mode” operation requires repetitive ON/OFF operations, with groups of concentrated optical signals separated by interleaved “quiet times.” Unfortunately, it happens that the requirements of such operations can only aggravate the signal transmission difficulties noted above.
In light of the above, it is an object of the present invention to provide a system for controlling optical signals that will consistently stabilize “burst mode” transmissions. Another object of the present invention is to provide a system for controlling optical signals that effectively eliminates unnecessary noise on a fiber-optic network by turning the light carrier source completely OFF when there is no optical signal transmission. Still another object of the present invention is to establish a fixed, same turn-on and turn-off time for every optical transmission regardless of the RF power in a particular input signal. Yet another object of the present invention is to have a predetermined optical power level for each optical transmission. Another object of the present invention is to provide a system for controlling optical signals that is easy to use, is simple to manufacture and is comparatively cost effective.